1. Field of the Invention
The present invention relates to a vehicle operable with muscle power and/or motor power, in particular an electric bicycle, and to a method for operating the vehicle operable with muscle power and/or motor power.
2. Description of the Related Art
Vehicles of this kind are known, for example, as electric bicycles having an additional electrical drive system, the electrical drive system being capable of assisting riding of the vehicle when pedaling, up to a predetermined maximum speed (e.g. 25 km/h). In such electric bicycles, the requirement can further exist for switching off the electrical drive system as soon as the rider ceases pedaling. Electric bicycles of this kind often encompass a sensor for determining a crank position and/or a rotation speed sensor for determining a rotation speed of the crank. With these sensors, a pedal standstill can be detected and shutoff of the electrical drive system can be initiated. An alternative to these sensors is based on an evaluation of a torque curve at the pedal shaft. A shutoff criterion here must be a rider torque applied by a rider is no longer being measured. Because of the top and bottom dead center points of the crank drive, a sinusoidal signal curve for rider torque can be sensed at the pedal shaft. This approach, however, would result in an undesired periodic shutoff of the electrical drive system at the bottom dead center point of the crank drive. In practice, therefore, a monitoring device is provided that starts a counter when the rider torque falls below a defined threshold. If the rider torque does not rise again within a defined, fixed time span, the electrical drive is shut off. The length of this predetermined time span is constant. As a result of this predetermined time span in which the electrical drive system is not yet interrupted, the electric bicycle continues to be driven by the electrical drive system even though the rider has ceased pedaling. This is perceived by many riders as obtrusive, however, since the electric bicycle does not immediately implement the rider's input. A further series of problems results in particular with hub gear systems, since run-on of the electrical drive system during shifting is unfavorable because with hub gear systems, a gear change cannot occur under high chain loads. The rider must therefore, after the cessation of pedaling, additionally wait for the predetermined time period until a successful gear change is possible. A reduction in the predetermined time span during which the electrical drive system continues to run also does not solve the problem, since assistance by the electrical drive system would be regularly interrupted in particular in a context of low and irregular pedaling frequencies with pronounced low points in the muscle-generated torque. This, however, results in very rough and uncomfortable riding behavior.